New with nodes in C, how to fix the struct? - c

Question

I have problems with understanding the whole concept of this. The major issue that confuses me is the the pointer inside a struct inside a struct... Basically what I understand is that I am wanting to create a chain of nodes.
When I run this program it crashes after two seconds. I believe there is something wrong with my structure in main.c, because I have created it by myself and as you can see I am really Bambi on thin ice over here...
main.c
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include "list.h"
// I guess my struct is not correct
static struct {
LIST node;
int item;
} node;
int main() {
list_create();
list_append(node.node, node.item);
}
list.h
typedef struct node* LIST;
LIST list_create (void);
void list_append (LIST l, int item);
list.c
struct node* list_create() {
struct node* head = (struct node*) malloc(sizeof (struct node));
head->next = NULL;
return head;
}
void list_append(struct node* n, int item)
{
/* Create new node */
struct node* new_node = (struct node*) malloc (sizeof (struct node));
new_node->item = item;
/* Find last link */
while (n->next) {
n = n->next;
}
/* Joint the new node */
new_node->next = NULL;
n->next = new_node;
}

Answer 1

At first, node is use for create a structure with data and in THIS data you have a pointer to another struct.
static struct {
LIST node;
int item;
} node;
Actually your structure is incorrect.
You must create at beginning a structure with your data for example :
static struct node{
int item;
};
then put a pointer to the similar structure but will not have same data =>
static struct node{
struct node *next;
int item;
};
You will can use this pointer to manipulate other & other structure.
I see another problem in your main :
You call the function "list_create()" which return a pointer to structure but you assign nothing.
you must create a pointer to struct then assign it like this :
int main() {
struct node *list;
list = list_create();
}

Answer 2

This code works completely (you can put it all in one C file; annotations in the code):
#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
/* I removed the "static", because what we want is a type,
not a global static variable */
/* This "node" is our list-element. It has a pointer to a next element, and
some data, in this case, an int. */
typedef struct node {
struct node *next;
int item;
} node;
/* For convenience, another type, a pointer to a node. */
typedef node *LIST;
/* Creating a list is as simple as creating a node, and make the "next"
pointer NULL, you got this correct. */
struct node* list_create() {
struct node* head = (struct node*) malloc(sizeof (struct node));
head->next = NULL;
return head;
}
/* Nothing wrong in this append code. */
void list_append(struct node* n, int item)
{
/* Create new node */
struct node* new_node = (struct node*) malloc (sizeof (struct node));
new_node->item = item;
/* Find last link */
while (n->next) {
n = n->next;
}
/* Joint the new node */
new_node->next = NULL;
n->next = new_node;
}
/* I added this to make sure it works :) */
void print_list(LIST l) {
LIST tmp = l;
while (tmp) {
printf("%d\n", tmp->item);
tmp = tmp->next;
}
/* Here are some changes. I create a local LIST (which is basically a pointer
to a node, remember?) and use list_create to initialise it. Then, I call
list_append two times to put some extra data into it.
Works perfectly! */
int main() {
LIST myList = list_create();
list_append(myList, 10);
list_append(myList, 13);
print_list(myList);
}

Answer 3

You are calling list_create, but not using its result.